There was this one time, at barista camp.... I was sitting with Vince Fedele, Nick Cho, and Peter Giuliano. And the conversation turned to the weighing of espresso as a determination of when the shot was finished, or prepared correctly. And Vince and Nick went back and forth, and I listened intently to see if I learned something new but what I surmised was this: Vince believes espresso should be weighed to determine it's completion and success, and does so at his home, and Nick believes it pure malarkey. I have to say, I tend to believe I need to understand the subject more to form a more solid opinion, but I have to say I think it's something that can be looked at further, but I don't see the need now. (And I'm sure by the time this thread ends, I will understand the need to/need not to, even more.)

My point is, and Anne Nylander brought it up today, that the majority of baristas out there don't have enough of a firm grasp of just the basics of espresso, what a good shot looks like, how to know when it's done, what the SCAA's standards for espresso are, which I know are in the process of being more hashed out by the Tech and Standards Committee. Right now, if we simply talked to baristas about weighing shots, we'd have a lot of 1.5oz water bombs, with a slight hint of coffee. And that's just the reality of it. I believe like Tonx that this is great lab stuff, but it's too soon to think this is practical in most shops and by placing emphasis on it as leaders, we're getting the cart before the horse for many people.

I'm all about finding new and exciting ways to make espresso better, don't get me wrong. I've changed my ideas and thoughts about coffee and how to make it over the years, and will in the future. It is an elusive thing, by nature, but I just don't understand myself how determining the shot is finished or made right by weighing it out. Enlighten me, and let's get this conversation going.

I think weight is a useful tool in determining consistency. This doesn't mean that all the other tools you currently use to evaluate espresso should be disregarded. If anything you should dial it like you normally would first, and then weigh shots that you're satisfied with to determine how much the good shots weigh. It is extremely difficult to eyeball the volume of espresso consistently every single time.

When you brew coffee in your Fetco, or Chemex, or v60 etc., you don't just eyeball the amount of coffee you use. You weigh it!

This comes from Fred Noble with Allegro Coffee. (He's not a member of coffeed yet.)

"I am not a physicist, i sell coffee for a living, lol. But water's density changes depending on quite a few factors. First, the temperature of the water. Boilers are not consistent across the industry. At boiling, a shot with a volume of 50cm cubed weighs 47.92 grams. That comes out to be about a 4% difference to what many call the standard. A lot of other pieces affect the overall weight of the shot, including impurities in the water, initial dry weight of the coffee (everyone's grinder would need to be spot on everywhere), tamping to the same pressure everywhere (i've worked in several companies and heard everything from 30# all the way to 45# as an individual company's standard), the pump pressure needs to be exact in every machine everywhere, and the temperature needs to be equal in every machine. As much as I am for moving our industry forward, the argument for weighing espresso sounds more like an argument created by a technician trying to make money calibrating everyone's equipment than it does an industry trying to come together to improve the final product that goes into people's mouths."

But I go back to my question via Twitter. Does espresso brew the same way coffee is brewed? If not, can we apply the same rules to espresso? Because of the variable of espresso (dosing, tamping, grind size) weighing out the espresso doesn't guarantee the shot is correct and finished. Am I wrong? Because I know from training that baristas shot will vary from shot to shot to shot to shot, not because of the volume, but the flow.

jason dominy wrote:weighing out the espresso doesn't guarantee the shot is correct and finished. Am I wrong?

No, this is true. No one is saying that weight determines quality. But you teach consistency above all else when it comes to dose, distribution, tamp, etc. If you are consistent in preparation, the shots you like the best should all weigh about the same. And judging a shot based on looks isn't as consistent as weight. If you were to go into your lab tomorrow and weigh 20 shots in a row that were prepared "traditionally" I suspect the range would vary quite a bit.

Fred Noble's comments may be accurate, but useful mostly in regards to comparison between machines, shops, and baristas. For all intents and purposes, this discussion is about what one barista is doing consistently.

jason dominy wrote:And Vince and Nick went back and forth, and I listened intently to see if I learned something new but what I surmised was this: Vince believes espresso should be weighed to determine it's completion and success, and does so at his home, and Nick believes it pure malarkey.

For the record, I never said, nor thought "pure malarkey." I do believe it's semi-malarkey though.

Mass is a constant. Volume, is mass x density, which means that volume will be dependent on density. Mass is dependent on matter either being there or not, which is like saying mass is dependent on mass. The point that Andy Schecter was bringing up a few years ago (when he was the first to really be making noise out there about this) was that scientifically, using volume to determine the completion or quality of a shot is a fallacy. Espresso extracant can vary greatly in density. That means that the volume can vary greatly, for the same given mass. Therefore, the only way to truly and accurately measure the amount of extraction is to measure by mass. This is absolutely true, and scientifically indisputable.

My beef with this has to do with practical, real-world application. I could get into a long debate or diatribe about the practical validity of using mass as a qualitative metric in espresso extraction, but the fact is that we're really after the most delicious shot, right? My point is: A barista has enough information to pull an excellent shot of espresso if and only if they learn to correlate the visual appearance through the extraction with the taste of the final beverage. Furthermore, using mass to measure the extraction may help aid a barista in her or his education, or, in fact, hinder their development, depending on how they're trained.

Two points about this.

1) I do not train baristas to use clocks to time shots, except as a secondary tool. I train baristas to very closely watch and analyze the streams visually, and learn to correlate what they see with how it tastes. "Clockwatching" is not a good practice. Neither would "Scalewatching" be.

2) Whether thinking about mass as a measurement for extraction, or using a tool like the Brewing Control Chart and ExtractMojo, there's an important principle that baristas need to understand about the relevant correlation: - If you brew a cup of coffee that's "truly delicious" and well-balanced and full-flavored and pleasing in body and such and such, there's a very good chance that if you did the measurements, you'd end up in the "proper" zone on the Brewing Control Chart.- If you brew a cup of coffee and do the measurements and you end up in the "proper" zone on the chart, that does not necessarily mean you have a "truly delicious" cup of coffee. ESPECIALLY with some of the newly-popularized manual brewing methods, it is very possible (if not probable) that a barista brews a cup that lands in the Gold Cup zone on the brew chart, but tastes out-of-whack. Why? Because many baristas are brewing un-balanced cups (part overextracted, part underextracted), especially on tools like the Hario V60.- Using mass as a tool for consistency or quality of extraction is similar. Mass is one piece of information, and it is scientifically relevant. But if taste is the ultimate arbiter of quality, mass becomes practically less relevant. Not to mention, if mass is consistent from shot to shot, that does not mean that the taste of the shot is consistent. The correlation may work the other way around though.

So yeah. Semi-malarkey.

Last edited by nick on Sun Oct 31, 2010 7:32 am, edited 1 time in total.

nick wrote: A barista has enough information to pull an excellent shot of espresso if and only if they learn to correlate the visual appearance through the extraction with the taste of the final beverage.

Regarding real-world application I personally am only advocating the collection of as much data as possible, and mass provides significant data that could be (more) easily collected.

nick wrote:Therefore, the only way to truly and accurately measure the amount of extraction is to measure by mass.

This is the one thing you said I agree with.

By having a floating time, you are allowing for changes in coffee chemistry you can't measure to go after a specific extraction percentage. It seems backwards to have two real variables when you are arguing about consistency. Wouldn't it make more sense to 'fix' all the variables including time to tight ranges and make grind (volume) the only adjustable variable. I would rather have a little variation in volume (which can be tweaked shot to shot by grind) than a range of variation in time. The idea of weighing dose and looking for off color indicators to avoid channeling is basic and assumed. Assuming understanding and observance of errors in method, then espresso is repetition. We do everything with purpose from flushing for a few seconds, to drying the pf, why not use a clock to confirm the repetition when trying to dial in to that previous ideal shot? A timer is more useful than weighing the end results any day of the week.

Where weighing your shots seems most reasonable is in a setting where coffees are not rested or go between widely varying rest dates. Our philosophy is to know what the rest date means and include that in the brewing equation so as to avoid confusion over volumes. All this previous commentary assumes a single already dialed in coffee though everything would be different if rotating through a bunch of coffees in a roulette style bar with different rests and roaster styles.

To your v60 commentary, sure the majority are not very repeatable (including the methods you posted). The problem remains, methods without a firm methodology. Extraction percentage is red herring, doesn't help for a v60 because you can simultaneously over and under in the same cup. The problem is the lack of a widespread tool that makes brewing at different temperatures/flow rates/volumes/doses easier (like the Luminairecoffee project). As long as it is fully manual, people will do it a myriad of ways that are maybe too art focused and hard to repeat.

Everyone says this but that's not what is happening out there in regards to weight and TDS. Tools that are good as a consistency check once every so often are now interfering with our tasting process. People are being encouraged to use these tools as a measure of quality and made to second guess the taste results. Measure first, taste later is the current mantra.

Has anyone ever questioned why we use TDS derived calibration tools that make no effort to account for water quality and it's effect on coffee chemistry?

I wanted to interject with a little catching up, for those of us playing along at home.

This is from Sarah Leslie, my assistant:

"I was never trained to weigh shots until I was preparing for the 2010 NERBC. I spoke with Sammy Piccolo over the phone and he gave me some advice about my espresso and my routine. He advised that I weigh my shots as I practiced so that I could determine the brew ratio. This is mainly a way to more deeply understand the espresso you are working with and what's happening in the extraction. It's also a great way to make sure you are dosing consistently and getting the same results each time.

So to find the brew ratio you take (D / S) x 100 = % where D= dry weight of espresso in the portafilter and S=shot weight after extraction. You can go here http://www.jimseven.com/2007/01/02/espr ... on-ratios/ to read more about brew ratios and why James Hoffman thinks weighing your shots is the way to go.

Weighing shots to determine the brew ratio is a great way to get to know an espresso, work on the consistency of your habits, and is a good way to communicate between other baristas how you are brewing your coffee. It's not something that should take the place of the Observe step of brewing espresso where you look for volume, color, and speed."

When I responded to this chatter on twitter yesterday, it was really to agree with tonx's sentiment that new espresso machines don't necessarily need built in scales. This is something I still stand behind.

It also does not mean I don't think there should be development of more useful tools for baristas. I am self-admittedly the opposite of an early adopter; in my opinion, if something works fine the way it is, why fix it. Then time and again, people come along and prove to me why the new technology is supremely useful.

I'm certainly like that with brewing coffee. I wish I could shed some of the steps I go through to brew a freaking cup of coffee at home - a takahiro kettle, rinsed paper, weighed water, weighed coffee fresh ground in a burr grinder... don't you wish that sometimes too? But I know that each step is crucial to making great coffee, similarly to getting very comfortable with weighing shots of espresso.

But a few things come to mind. First, is the basic tenets we instruct by at TT. We wrote about it here http://www.tamptamp.com/uncategorized/t ... damentals/, but the basic gist is that when we train, we hope our students go home with three foundations to explore coffee: cleanliness, taste, and repeatability. In our lab, we explore why there are rules, we think about about what factors of making espresso really influence taste. We get out scales and collaborate with our students - if they want to weigh their shots, fine, here's the scale. If you want to practice dosing out shot after shot, or managing your waste, go for it. We taste all kinds of espresso and coffee - good, bad, and ugly, to explore what "good" really means and how relative that is to first time tasters and expert tasters. We try to get students speaking in a common language about what coffee tastes like.

This is all fine and good, and I think to some extent what we all love about coffee - the conversation is possibly endless. Which leads me to point number 2.

Ellie Matuszak said something very important to me during my formative time starting up TampTamp, in regards to helping clients establish dedicated training programs. We were discussing whether or not it was valuable for me to make clients practice with me during a dedicated time, or if I should let baristas return to work to implement their skills more thoroughly. This is another tug-of-war, between labor costs, student information retention, and the need to be in a real-world environment to really utilize freshly learned skills. But I will never forget what she said to me: "The customer should never feel as though they are the ones being practiced on."

That is something that sticks with me, and each time a cafe or barista wants to implement an experimental system, I get wary. When I go to a restaurant, I don't want to know that the chef is "double checking" their work. I want to feel confident that they are doing their best to serve me the best thing that they can make - if they don't feel ready, then maybe they shouldn't be cooking. And the very last thing I want to do, is overhear two cooks arguing about whether or not the other one is doing it right - in front of me, who's paying a pretty penny for the meal!

The same goes for specialty coffee, and we are in an awkward position, as the ambassadors of this brown stuff, where we must both be the waiter and the chef in the same 3 square foot area. We must confidently present our craft, to the best of our ability and within our circumstances, without getting arrogant or haughty. It's a tough act to keep up consistently - and each time another gadget is added to the customer line of sight and barista workflow, it's another x-many seconds that the barista is not spending engaged with the customer, or even worse, engaged with a co-worker instead of the customer, is another second lost and another potentially lost opportunity. I believe that the workflow of the barista should be as smooth and flawless as anything, so that the guest never needs to realize that "real" work was being done at all. It never feels that way in a fine dining restaurant. They are there to make you enjoy eating your meal - not teach you how the meal was made.

So do I think that weighing shots is a valid way to measure extractions? Yes, within its context. Is visually observing shots also very important? Yes, of course - we could argue that volumetric espresso machines have been serving "correct" espressos for a long time otherwise (uh, they haven't been). Do I think that more gadgets, or experimental barista tools should get added to the espresso bar?

If the systems are in place, the baristas are prepared and ready to implement the system, and the customers won't notice a change except better quality, then of course. Have at it. Otherwise, take a few steps back and think about how to execute the plan in a way that puts your customers first.

Does weighing the final shot detract anything from espresso itself? Does it hinder the quality and aesthetic of what is being served? Will customers at our shops, who already see us meticulously preparing coffee using a laundry list of QA skills, be put off by the sight of scales weighing espresso shots? I cannot think of a single instance in which this would be so. At worst it is neutral in those respects. At best, however, we as purveyors stand to a) broaden our understanding of the whole process while tightening our skill set in what is still pretty much terra incognita for many baristas and b) give another set of data points to collaborate on with other baristas. And the craft advances.

I weigh dry grounds in the pf every morning we open the shop. I get my trusty Jennings scale and my Polder timer and pull six or seven shots, weighing the dry grounds, then tracking the time of the shots. I do this to find the sweet spot for that espresso for the day vis-a-vis the roast age. Then I put away the scale/timer. Why? Because I've weighed and timed enough coffee and shots in my eight years behind bar to know pretty well what, say, 20.5 g of dry coffee look like and what 25-29 seconds is like.

Adopting after weight of liquid is no more difficult or burdensome than those other steps but has a potential lovely upside. And once you become familiar with what 32 g of liquid looks like (accounting for crema fluffiness/roast date) you won't need to look at the scale every single time.

We use timers/scales on the manual brew bar. Timers will never go away since it's obviously impossible to count those couple-three minutes in your mind while having customer conversations and whatnot. But I hope for the day that my skillset is so tight that I don't NEED the scales. Lord knows the cafe aesthetic for customers will go from pure science lab to more of an art museum. We are still doing our calculations, but under the surface. Out of sight from the customers.

Nobody complains about timered grinders or a PID display that gives us temp info or a pressure gauge for steam and shots, or shot timers. All but the dullest of baristas knows that these are guides, not doctrines to be bent on pain of death and hell.

I say, what will it hurt versus what are the potential upsides? Asking that gives us the strong indication that we only stand to open ourselves to greater consistency of taste, which is the holy grail--the whole point--of espresso, is it not?

This is from Jackson O'Brien, a barista friend of mine in Nashville:"See, now I'm both a math nerd and a coffee professional, so this is something that hits near and dear to my heart.

In my heady days of home-espresso-machine ownership, I attempted to derive the absolute equation for the best possible shot I could get, which I determined as being 17 grams with my capresso infinity set to the third finest grind setting tamped at 25 lbs of pressure completely evenly parallel with the counter, extracted after a 3 second temperature surf on a Rancillio Sylvia after a 30 minute heat up time (18 grams in the dryer winter months). I longed for a PID to accurately gauge my temperature and for a tamp equipped with a level so that I could ensure a further structured environment.

In the mean time, I was tormented by my bar shifts, where I'd make dozens of shots at a stretch where I didn't know my dose, didn't know my machine's temp, didn't know my dose weight, and didn't know my tamp pressure. The scientist in me knew that everything held equally would produce even results, but there was no way of knowing whether I (or any of my fellow baristas) were maintaining the same exact formula every time. (Not to mention the various unknowable factors when you have two finely tuned pieces of metal smashing a coffee bean into 1200 odd pieces several thousand times a day. Do they heat up and expand causing the grind to be finer? Is the pressure of the beans in the hopper a factor?)

Given a gram scale, a good brewing device, and a recipe, it's generally possible for anyone to brew a great cup of brewed coffee, and similarly if you're able to measure and calibrate every last aspect of the espresso brewing process, anyone could pull a great shot, but ultimately if you're dealing with a shop that has any kind of real volume, that's not terribly possible, and in as much, one has to abandon science for art. If you're in a position where you can weigh out every shot, good for you, you've successfully eliminated one of the many many variables that go into making a great shot; in the mean time however, all of us need to rely on people who will instinctively know a great shot by the feel of the grinds beneath their tamp, by the look of the shot as it extracts, and most importantly the taste of the shots they're lucky enough to sample.

Of course, someone could design a grinder/tamper/espresso machine that was able to weigh out specific amounts of coffee to be ground, grind it (calibrating for wear and tear on the burrs), tamp it with a certain amount of pressure and extract it for a certain amount of time and get a perfect shot every time, but who wants to put their faith in machines? By and large, I've met many robots that were stronger and faster than people, but few that are as smart, and none that had any sort of good taste, and that's ultimately what it boils down to."

jason dominy wrote:I just don't understand myself how determining the shot is finished or made right by weighing it out.

As far as I know, weighing out a shot never turned a lousy one into a good one!

The point is, once you've tweaked your parameters and pulled an excellent shot, measuring the shot by weight (ie, grams of espresso beverage) rather than by volume will allow you to accurately share your "recipe" with others. Since the volume of an espresso shot varies greatly depending on the age of the beans, type of portafilter, etc, a recipe using volumetric measurements for espresso is practically useless.

For example, here's Barismo's recipe for pulling shots with their Soma espresso blend:

Pull 19 grams for 26-28 seconds at 201.5°F, total volume 1.25 to 1.75oz.

It doesn't say how many days off roast, or whether they use a bottomless or spouted pf. IMHO, such recipes are too vague to be useful. If they simply substituted, "shot weight 25-27 grams" instead of the "1.25 to 1.75 oz," we'd instantly have a clear picture of the type of shot Barismo is pulling. We know if it's in the super-ristretto style, a more dilute "normale," or somewhere in between.

It's not just Barismo that makes this mistake, of course. Most of the Big Names do the same (although a few roasters, to their credit, do it right).

Of course when Nick specifies an espresso recipe, it's this one: "Dose to taste, grind to taste, adjust temperature to taste, adjust shot volume to taste." That's cool, but some people need a little more specific advice.

Fred Noble wrote:As much as I am for moving our industry forward, the argument for weighing espresso sounds more like an argument created by a technician trying to make money calibrating everyone's equipment than it does an industry trying to come together to improve the final product that goes into people's mouths."

I wholeheartedly disagree with Fred's statement. To the contrary, accurately communicating about espresso technique is very much about people coming together to improve the final product. And since every competent cafe already has a gram scale used for periodically weighing out doses, specifying beverage weights has absolutely nothing to do with technicians trying to make money.

nick wrote:1) I do not train baristas to use clocks to time shots, except as a secondary tool. I train baristas to very closely watch and analyze the streams visually, and learn to correlate what they see with how it tastes. "Clockwatching" is not a good practice. Neither would "Scalewatching" be.

Agree 100%. A barista develops his or her skill far more quickly watching how the shot develops and tastes rather than watching a clock or scale.

Jaime van Schyndel wrote:Tools that are good as a consistency check once every so often are now interfering with our tasting process. People are being encouraged to use these tools as a measure of quality and made to second guess the taste results.

A story went around about some guy at one of the coffee shows who refused to taste a coffee unless it had been first analyzed for extraction yield and found to be within his acceptable range. :-0 This is so absurd on the one hand, and so horrifying on the other, that one has to laugh and cry at the same time! But I don't believe this is at all widespread among people who genuinely love and understand specialty coffee.

First of all - we really, really need to stop this ridiculous pretend argument that pitches measurement against taste.

No one is advocating discounting tasting as part of dialling in, or as part of QC during service. However, every single time we start discussing measuring espresso in new ways - be it scales or extraction percentages - lots of people who should know better start arguing against it along these lines. Enough please.

I was trained, like every body here, to judge an espresso extraction based on colour, flow rate/brew time and consistency and to correlate it to taste. I was, like a lot of people, regularly encountering many different frustrations within espresso brewing relating to control and consistency.

We all accept that the look of a pour is a poor visual indicator to make serious assessments with. The impact of grinder, water, roast age, roast development etc etc all impact the look of a pour meaning that an identical flow rate of water through the coffee bed can look dramatically different due to some of these factors.

There is something else we need to accept here. Most of our current methodologies for brewing espresso aren't working. Even the best shops struggle with consistency. Does anyone here think that their shop is absolutely nailing 95%+ of the espressos they put out? Would you be willing to bet that if someone walked in and judged your entire business on a single shot of espresso that they'd get the exact experience you would want them to have?

We, as an industry, need to improve. Now more than ever. I don't want to childishly bash our own industry, I am proud to be a part of it, but I want to see it achieve greater success.

Replacing volume of espresso with weight of espresso is a good thing. It is a consistent and valuable metric in the brewing process whose impact can, to some extent, be accurately predicted and understood.

Both communicating and, more importantly, replicating a brew recipe that has been determined by taste is significantly easier and more productive when using brew weight. If anyone has a convincing argument against this then I would welcome that.

I don't really understand why people don't want more information about their brewing process - be it espresso weights or understanding their coffee better using stuff like Extract Mojo. I don't want to imply that the skills people develop around coffee brewing aren't important nor imply that robotic production is the way to go. I've seen many people roast batches of coffee using a minimal amount of information outside of the trier. I am impressed, but at the same time if I had 200 batches of production to do and I wanted to replicate my preferred roast then I'd want lots of info available.

Discounting this because people might become scale watchers, like people are already clockwatchers, or because it might be misused in other ways is wrong. Misuse doesn't invalidate a technology or an idea. Maybe there is a mythical creature roaming the coffee industry, craving coffee but unable to find any that passes its technical extraction requirement before it passes its lips. So what? There are always going to be people that detach the technical from the sensory. It doesn't mean that there is no opportunity to marry the two and achieve success as a result.

Beautifully put James. I have to wonder (this is NOT directed at anyone, here or otherwise) if some of the reaction to this is out of fear, lack of understanding, and worry that a less esoteric methodology might level the playing field between the experts and bar baristas. Not an accusation,just trying to figure out why there is so much resistance to something that is a simple, useful tool to understanding one of the parts of maintaining quality. I've found weighing shots to be a vital second step in training baristi after they have basic espresso skill. It gives them a way to answer questions that come up, and is important to fully utilizing dose controlled grinders to the fullest potential.

Well said. Still, people tend to become reliant on technology to make their lives easier and sometimes better. Would we all have better penmanship and spelling without typewriters and spell check? Maybe. I am thankful for most of what technology brings us. The dependence I can do without. When I train new Baristas, I focus on controlling the variables that make up the process. If you do the same thing every time and your equipment is not at fault, turn to your grinder and adjust. The tools at our disposal today are keen. Lets use them as measuring instruments like they were designed as. Too many people are starting to use them as a determination of quality. If you are focused on only one or two measurements as your guide to a great espresso, you are missing out on the bigger picture. Remember that one of the 4M's in Mano- the hand or skill of the Barista. I suggest using every tool you have available to dial in your shots much like you have to season the pf every morning. When you are struggling with your extractions pull out your mojo if you like, just use it as a guide not as the be-all to end-all.

OK. So it seems to me the major benefit of weighing espresso is overcoming the difficulty in assessing volume when crema is involved. Right? I mean, everyone throws around the 4% volume variance thing, but that variance is between room-temperature water and 200 degree water, but that's not a real-world circumstance. It's the difference between 195 and 205 degree water, which must be significantly smaller than 1%.

So its not about temperature/volume variance, it's about crema, and assessing true volume when foams are involved. I agree that is difficult. Weighing output is an easier way to normalize.

Here's another easy way- measure the volume of the water being used. Although they have now fallen out of fashion, "automatic" espresso machines (those which have "single" and "double" buttons) measure the water going through the grouphead volumetrically. Certainly that would be easier than incorporating a scale, right? Of course that would require us to restate our "recipes" for extraction as "weight of coffee/water volume in" just as everyone is now grappling with the change to "weight of coffee/espresso weight out".

Peter G wrote:everyone throws around the 4% volume variance thing, but that variance is between room-temperature water and 200 degree water, but that's not a real-world circumstance.

Just because I thought you'd be interested: according to Vince, the otherwise brilliant Doctor Lockhart from the Coffee Brewing Institute forgot about the "4% volume variance thing" in his seminal extraction yield studies. This resulted in an error in his calculations: his brewing preference range, which he believed to center around 20% extraction yield, is actually centered at 19% when properly calculated.

So the variance of volume with temperature isn't particularly important when measuring the amount of warm espresso, but it's important in other contexts.

Peter G wrote: So it seems to me the major benefit of weighing espresso is overcoming the difficulty in assessing volume when crema is involved....Right?

Right.

Peter G wrote:Here's another easy way- measure the volume of the water being used. Although they have now fallen out of fashion, "automatic" espresso machines (those which have "single" and "double" buttons) measure the water going through the grouphead volumetrically. Certainly that would be easier than incorporating a scale, right? Of course that would require us to restate our "recipes" for extraction as "weight of coffee/water volume in" just as everyone is now grappling with the change to "weight of coffee/espresso weight out".

Yes, this works, but with two caveats:(1) The accuracy of the "recipe" will vary from machine to machine and from basket to basket. That's because the amount of water lost into the puck or into the drain varies depending on the amount of headspace above the puck in your machine (and a few other factors).(2) Weight of coffee/weight of espresso give the barista more information: she immediately knows how "ristretto" or how "lungo" the shot is, and it gives her 2 out of the 3 pieces of information needed to calculate extraction yield if she chooses to do so.